Determination of J/ψ leptonic branching fraction via ψ(2S)→π+π−J/ψ

Le résumé fourni par la source

A comparison of the rates for $\ensuremath{\psi}(2S)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi},$ $J/\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\psi}}{l}^{+}{l}^{\ensuremath{-}}$ and $J/\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\psi}}$ anything is used to determine the $J/\ensuremath{\psi}$ leptonic branching fractions. The results are $B(J/\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\psi}}{e}^{+}{e}^{\ensuremath{-}})=(5.90\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\pm\else\textpm\fi{}0.10)%$ and $B(J/\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\psi}}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})=(5.84\ifmmode\pm\else\textpm\fi{}0.06\ifmmode\pm\else\textpm\fi{}0.10)%,$ where the first error is statistical and the second is systematic. Assuming lepton universality, the leptonic branching fraction of the $J/\ensuremath{\psi}$ is $B(J/\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\psi}}{l}^{+}{l}^{\ensuremath{-}})=(5.87\ifmmode\pm\else\textpm\fi{}0.04\ifmmode\pm\else\textpm\fi{}0.09)%$ per species. This result is used to estimate the QCD scale factor ${\ensuremath{\Lambda}}_{\mathrm{MS}\ifmmode\bar\else\textasciimacron\fi{}}^{(4)}$ and the strong coupling constant ${\ensuremath{\alpha}}_{s}.$

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